Borosilicate glass composition

ABSTRACT

AN OPTICAL GLASS COMPOSITION IS DISCLOSED WHICH CONSISTS ESSENTIALLY OF 42 TO 52 MOLE PERCENT OF THE GLASS FORMERS B2O3 AND SIO2 WITH THE MOLE RATIO OF B2O3 TO SIO2 RANGING FROM 3, 4, 8. THE COMPOSITION FURTHER COMPRISES 36 TO 46 MOLE PERCENT OF THE OXIDES OF THE ELEMENTS OF THE GROUP OF ZINC, CADMIUM, LEAD AND LANTHANUM WITH THE PERCENTAGE OF ZINC OXIDE AND/OR CADMIUM OXIDE RANGING FROM 12 TO 22 MOLE PERCENT, THE PERCENTAGE OF LEAD OXIDE RANGING FROM 8 TO 24 MOLE PERCENT, AND THE PERCENTAGE OF LANTHANUM OXIDE RANGING FROM 2 TO 10 MOLE PERCENT. 10 TO 15 MOLE PERCENT OF AT LEAST THEE OXIDES OF THE ELEMENTS OF THE GROUP OF CALCIUM, ALUMINIUM, TITANIUM, ZIRCONIUM, AND TUNGSTEN.

United States Patent Int. Cl. @038 3/08, 3/10 US. Cl. 106-53 7 Claims ABSTRACT OF THE DISCLOSURE An optical glass composition is disclosed which consists essentially of 42 to 52 mole percent of the glass formers B 0 and SiO with the mole ratio of B 0 to SiO ranging from 3, 4 to 4, 8. The composition further comprises 36 to 46 mole percent of the oxides of the elements of the group of zinc, cadmium, lead and lanthanum with the percentage of zinc oxide and/or cadmium oxide ranging from 12 to 22 mole percent, the percentage of lead oxide ranging from 8 to 24 mole percent, and the percentage of lanthanum oxide ranging from 2 to 10 mole percent. 10 to 15 mole percent of at least three oxides of the elements of the group of calcium, aluminium, titanium, zirconium, and tungsten.

BACKGROUND OF THE INVENTION (1) Field of the invention The present invention relates to optical glass. More specifically the invention relates to a borosilicate glass composition.

(2) Description of the prior art In computing optical systems the dispersion values of the employed collecting and diverging lenses are of material importance to the chromatic correction. For this reason it is extremely diflicult to make use of the heavy flint glass compositions known in the art in combination with the highly lanthanum containing crown glasses which have been developed in recent years. In order to overcome this disadvantage a highly refractive glass composition had to be found, said glass having smaller dispersion than that of the known heavy flint glasses. In addition to these desired optical values the composition had also to possess those properties as are required by modern production methods, e.g. chemical stability, suitability for moulding etc.

SUMMARY OF THE INVENTION This goal is achieved by a glass composition which, according to our invention, consists of 42 to 52 mole percent of the glass formers B 0 and SiO with the mole ratio of B 0 to SiO ranging from 3,4 to 4,8. The composition further comprises 36 to 46 mole percent of the oxides of the elements of the group of zinc, cadmium, lead and lanthanum with the percentage of zinc oxide and/or cadimum oxide ranging from 12 to 22 mole per- 3,561,986 Patented Feb. 9, 1971 cent, the percentage of lead oxide ranging from 8 to 24 mole percent, and the percentage of lanthanum oxide ranging from 2 to 10 mole percent. 10 to 15 mole percent consist of at least three oxides of the elements of the group of calcium, aluminium, titanium, zirconium, and

tungsten. MgO, SrO and BaO are earth alkali oxide equivalents to CaO, as per teachings George X. Morey in Properties of Glass, 2nd edition, 1954, page 76. The

percentage of these oxides ranging as indicated below: Mole percent CaO 0-5 A1 0 0-3 TiO 0-4 ZI'Oz W0 0-3 DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following tables various examples of glass compositions according to our invention are listed together with their batch constituents and optical values.

Table 1 demonstrates the effect of replacing lead oxide by lanthanum oxide.

In the compositions listed in Table 2 major quantities 25 of Zinc oxide and lanthanum oxide are introduced while The glasses may easily be melted color poor and do not present any difficulties in further treatment. The content of barium oxide should be kept as low as possible, since barium oxide tends to make the glasses soft and sensitive to stains.

Preferably, the batch constituents are melted in a crucible of platinum at temperatures ranging up to 1100 C. Refining takes place at temperatures up to 1300 C. After said refining the melts are stirred continuously while cooling to cast temperature of approximately 800 C. The glasses are then poured into slightly warm steel moulds.

As is well known in the art small quantities of arsenic trioxide and oxide of antimony may be added for color improvement.

A specific example how to melt a glass composition according to our invention is as follows:

A glass batch according to the Examples 1 or 9 of a total weight of 4 kp. is melted at 1000 C. in a crucible of platinum. Thereafter it is refined for minutes at 1200 C. When the temperature has decreased to 1170 C. the melt is stirred for 50 minutes and then, while continuously being stirred, the melt is cooled to 780 C. At that temperature the glass is cast into steel moulds, the latter being pre-heated to 550 C. Further cooling and annealing is accomplished in customary manner. The transformation point of this glass is at 480 C., the softening point at 522 C. The glass has a coefiicient of expansion of 6,4)(10 in the temperature range from to C. The optical values are n =1,8430 and v =30,0.

TABLE 1 Example Percent Percent Percent Percent Percent Percent by Mole by Mole by Mole by Mole by Mole by Mole weight percent weight percent weight percent weight percent weight percent weight percent 20. 0 35. 5 20. 0 85. 8 20. 0 35. 8 20. 0 36. 0 20. 0 36. 2 20. 0 36. 3

TABLE 2 Example percent percent b M e by Mole weight percent weight percent TABLE 3 Example percent percent percent by Mole by Mole b Mole weight percent weight percent weight percent "i6f6"" 15fi"""i6.'6"""ifi' "ifti ili 40. 0 22. 4 40. 0 20. 9 40. 0 21. 2 12. 5 4. 7 7. 5 2. 7 7. 5 2. 7 4.2 4.3 4.2 4.0 4.2 4.0 2.0 3.1 2.0 2.9 2.0 2.9 4.5 2.4 4.5 2.2 4.5 2.2 1.8 2.2 1.8 2.1 1.8 2.1

"""" "ii63"""""'"ifi'""'"'""'ifii""" Having fully disclosed the invention, what is claimed is: 1. A borosilicate glass composition the melt combination consisting in mole percent of:

Mole percent B 0 35 5 SiO 103 ZnO 15.1 PbO 22.4 La O 4.7 ZrO 4.3 T102 3.1 W0 2.4 A1 0 2.2

with n being 1.8430 and v being 30.0.

2. A borosilicate glass composition the melt combination consisting in mole percent of:

Mole percent B 0 35.8 SiO 10.3 ZnO 15.1 PbO 21.0 Lagog 5.9 Z102 4.2 T10 3.1 W0 2.4 A1 0 2.2

with n being 1.8412 and v being 30.4.

3. A borosilicate glass composition the melt combination consisting in mole percent of:

Mole percent B203 35.8 $10 10.4 ZnO 15.2 PbO 19.7 La O 6.8 zro 4.3 Tio 3.1 wo 2.4 A1203 2.3

with n being 1.8396 and v being 31.0.

4. A borosilicate glass composition the melt combination consisting in mole percent of Mole percent B 0 36 0 S10 ZnO 15.3

PbO 18.3

La O 7.7 ZIO 4.3 T10 3.2 W0 2.4 A1 0 2.3

with n being 1.8387 and v being 31.2.

5. A borosilicate glass composition the melt combination consisting in mole percent of:

with n being 1.8365 and v being 32.3.

6. A borosilicate glass composition the melt combination consisting in mole percent of:

Mole percent B 0 36.3 Si0 10.6 ZnO 15.4 PbO 15.7 Lagos 9.8 ZIOZ 4-3 TiO 3.2 W0 2.4 A1 0 2.3

with n being 1.8352 and v being 33.0.

7. A borosilicate glass composition the melt combination consisting in mole percent of:

Mole percent B 0 35.5 $10 10.3 Z 15.1 PbO 22.4 1.73.203 4.7 ZI'OZ 4-3 T102 3.1 W0 2.4 A1 0 2.2

with n being 1.8403 and v being 30.0.

References Cited UNITED STATES PATENTS 2,678,281 5/1954 Geifcken et a1 10653 2,899,322 8/ 1959 Brtimer et al 10647 3,043,702 7/1962 Bromer etal. 10653 3,149,984 9/1964 Faulstich 10647 FOREIGN PATENTS 783,110 9/1957 Great Britain 10653 HELEN M. MCCARTHY, Primary Examiner 

